Packages maintain the cleanliness and sterility of the product within from the manufacturing plant through transport, shelf life, and storage. Testing of the quality of seal and package integrity is of paramount importance in any packaging industry. For example, the quality of the seal and integrity of a package dictates the shelf life of food products (e.g., chips, frozen foods, children's beverage/juice packages, meat, dairy products, and fresh vegetables), medical products (e.g., pharmaceuticals), and cosmetic products (e.g., skin care and makeup).
ISO (International Organization for Standardization) and ASTM (originally known as the American Society for Testing and Materials) standards provide guidance for manufacturers to ensure package integrity and quality and the sterility and shelf life of the products within.
Package testing includes ensuring the integrity of the sealed package, and assuring that no weaknesses in the sealed areas of the package permit leaks to develop with handling stresses and time. Package integrity testing can be referred to as a “leak test” of the package. That is, package integrity testing determines whether there is a failure in the materials or process that allows contamination to enter. Seal strength testing, on the other hand, measures an attribute of the seal, which is designed to ensure that the seal presents a barrier to at least the same extent as the rest of the package. Both integrity and seal testing are important aspects of ensuring proper packaging.
Seal strength testing may include tensile stress testing (peel strength of the seal), which is used for packages with peel-open pouches, and inflation tests such as burst and creep testing, which are commonly used for testing both peelable and non-peelable seals. However, these tests, particularly the tensile stress test and the burst test, are typically destructive tests, requiring the rupturing of a package under test.
Specifically, the inflation tests typically require pressurizing the entire pouch and measuring the peak rupture pressure (burst test) or the time to failure at a constantly held pressure (creep test). The inflation tests provide peel stress with horizontal and vertical components, tension due to hoop stress in the vertical direction, and lateral stress due to package expansion. If these stresses are greater than the strength of the seal at any point within the package, the seal will rupture. When a seal is good, the base material will typically rupture before the seals will release in an inflation test. In a bad seal, a fracture or delamination of the laminate may be encountered in the seal area.
Package integrity testing is a measure of the package's barrier material and seal, providing a “leak test” of the whole package. In addition to seal bonding failures or disrupted seals, leakage can be the result of large holes, pinholes or cracks in package materials. Either source of leakage represents the potential for product contamination from elements of the ambient atmosphere outside of the package entering the package, and the potential for the materials inside the package to escape.
There are a number of commonly used physical tests for package integrity, including the visual inspection method, the internal pressure method (e.g., bubble testing), the vacuum leak method (in which the package is submerged in water inside a vacuum chamber and escaping bubbles are observed), and trace gas detection, where the package is pressurized with a gas other than air and then examined for escaping gas with a gas leak detector. However, these tests tend to be subjective and non-quantitative, and in some cases messy and difficult to perform.
An alternative method that overcomes these objections is the pressure (or vacuum) decay test. In particular, the pressure decay method is often used to perform package integrity (leak) testing on flexible pouches or other packages that have non-porous material surfaces and seals.
The pressure decay test is accomplished by pressurizing the package to a fixed pressure, shutting off the pressure and connecting a pressure transducer. After a settle time, any observed changes in pressure may indicate the presence of leakage paths in the package seals or pinholes in the surfaces. This leak may be represented in decay pressure units or calculated leak rate units. The pressure decay leak test cycle, from beginning to end, includes the time to engage the package with the measuring instrument, a charge time for pressurizing the package to a predetermined test pressure, a settle time for allowing the volume of the pressurized package to change and then stabilize due to the stresses introduced by pressurization and adiabatic temperature changes, a test time for actually measuring the decay of pressure, and an unloading time for unloading the package from the instrument. Vacuum decay testing functions identically to the positive pressure decay test cycle, and can also be a time consuming process. Furthermore, pressure decay testing supposes that a test package or pouch can be pressurized, and is generally a destructive test.
If the package is closed or sealed so it cannot be pressurized from an external source, an alternative method of pressure decay leak testing involves creating a closed space around the test package, creating a surrogate chamber, and pressurizing (or evacuating) the closed space. Air entering the package through a leak (or in the case of a vacuum test, leaving the package through the leak) provides the measurement of leakage. This method is effective for non-porous pouch-form packages, shaped pouches, trays, and uniquely shaped thermoformed containers with induction welded seals. When a sealed package is placed in a surrogate chamber, a pressure differential can be created across the non-porous barrier package walls and seals. Once stabilized, air movement from the higher pressure to the lower will indicate the presence of a leak path, providing a quantitative measure of package integrity without disrupting the package seals. Leakage is measured by the pressure change in the vacant chamber space surrounding the package.
Although many package testing procedures exist, many of these tests involve destructive methods that are not adaptable to in-line testing. Therefore, test packaging or off-line samples are utilized for the testing, making it difficult to ensure the in-line packages are reliable and/or requiring a reduced yield in order to provide sufficient samples for off-line testing.
In addition, the current non-destructive tests are time consuming, also resulting in reduced yield or fewer packages being tested on-line.
Accordingly, there is a need in the art for fast, reliable integrity and quality of seal testing that can be performed in-line with packaging a product.